Random Noise


The NuForce P-20 Preamplifier



I work for NuForce (oft-stated fact) and I’m writing about a NuForce product (also oft-stated). Readers will question my impartiality, and so they should. I am decidedly partial, having been much impressed by NuForce amplification and its piddling power demands before I signed on. In a pre-employment review I expressed a preference for NuForce monos to a pair of yacht anchors that idled apiece at 200 watts. The relatively tiny NuForce pair was smoother, better resolved and every bit as perky.

So never mind what I have to say (tho I’d love you to read on). I fully expect disinterested reviewers to find much to admire and little, if anything, to criticize. Meanwhile, think of this as a press release.
The P-20 delights the eye. Its angled face is of a piece with the company’s high-end gear. (NuForce identifies its lines as Consumer and High-end.) The P-20 shares the Reference 18 mono amp’s under-three-inch height and seventeen-inch width – twice as wide as my CDP-8 player-transport and DAC-9 converter’s similarly sculpted cases.

The single, wide-chassis P-20 replaces the twin-box P-9. I wasn’t a big fan of the predecessor’s volume layout. With the P-9 set to operate in a dimmed mode, the illuminated panel would alternate between dim and bright when the volume setting straddled levels – an annoyance having no effect on the sound. (Anyone on the prowl for a closeout deal could do worse.) In keeping with the NuForce standard, the P-9’s resolution, transparency and lifelike presentation are exemplary.The P-20 goes a step beyond. (It’s a matter of ongoing fascination that what we perceive as great sound proves infinitely elastic. Among audiophiles, no difference for the better is ever shrugged off as negligible.)

Consistent with the CDP-8 transport, DAC-9 converter and Ref 18 amp’s touch-sensitive panels, the P-20’s panel replaces the P-9’s knobs. Tasteful red-on-black displays accompany turn-on and turn-off. (The DAC-9 retains a small knob: a volume control for its headphone amp.)

The sound of a factory-fresh unit: opaque. No surprise. In a hi-rez system, immature gear sits like a zit. Given the P-20’s stated improvements, I knew enough to bide my time.

I hear the properly seasoned preamp’s merits as heightened resolution, transparency and dynamic finesse, which operate together as soundstage enhancements. I have a better sense of the music’s strands. Transients and attacks are scalpel-sharp. A good recording more closely imitates life than anything I’ve experienced in this listening room. The preamp is not forgiving, however. Forgiveness, which is to say euphonious coloration, is not a quality I’ve valued or sought. The truth-telling Sasha W/Ps tell me all I need to know about events upstream. A great recording sings. Mediocrities croak.)

Recent and related tweaks: I replaced the P-20’s fuse with a Hi-Fi Tuning equivalent. These little wonders also occupy my Ref 18 amps (fuses earlier covered here). I’ve augmented the speakers’ WP Supreme Quantum chips with the same German maker’s cable chips. I’m delighted with what I hear but have made no recent A/B comparisons. (Another reason not to take me too seriously. I’m lazy.)


The Website’sP-20 statement and specs:
The P-20 Preamplifier’s elegantly sculpted aluminum case encloses a number of significant advances over the preamp’s award-winning P-9 predecessor in several key areas, especially with respect to volume control. A preamp’s volume-control capabilities are among its most critical features. In practical terms, we saw room for improvement over the already excellent P-9’s volume control within the areas of transparency and noise.

The P-20’s numerically controlled, switched-resistor ladder network features the last word in thin-film technology. In order to improve precision and lower the noise floor to the vanishing point, we’ve implemented a single thin-film, ultra-low-noise resistor in the signal path for each of the volume control’s 0.5 dB gain settings, thus permitting the listener to achieve the desired volume level in precise 0.5 dB steps. As a further benefit, the listener is able to adjust any input’s level to exactly correspond with any other, thereby simplifying the matching of source-component volume levels.

The heart of the P-20 boasts an all-discrete, fastidiously precise amplifier module. Because speed is of paramount significance, we’ve reduced capacitive loading on the final voltage amp with the implementation of ultra-low-noise, monolithic dual JFETs, specially selected VMOS FETs, and extremely flat hFE bipolar transistors in a dual cascode configuration, all of which are combined within a driven-shield arrangement. The P-20 offers a 5 MHz power bandwidth, an S/N ratio exceeding 100 dB, and a dynamic range in excess of 120 dB. There are no capacitors or DC-servos in the inherently stable P-20’s gain circuit.

And, in keeping with these advances, we’ve paid a great deal of attention to isolation. We’ve covered the amplifier modules with thermal insulation along with heavy copper shields in order to avoid thermal drift or signal-degrading heating effects. Each amp module’s self-contained shunt regulator further assists in isolation from power supplies. A similarly isolated floating-current source supply feeds each module to insure separation from ground-system noise.

Since all control functions are powered by discrete power supplies, the P-20’s design prevents any logic circuitry clock-signal noise from ever contaminating the analog section's low-level signals. In keeping with the P-20’s state-of-the-art features, we include a delightfully convenient, custom-designed remote control. In sum, the P-20’s near-to-molecular clarity offers the last word in utterly transparent, organic sound – in effect, a stress-free listening experience as close to live as audio permits. Better still, these features can be activated by a 12V trigger signal enabling system integration without the need for manual intervention. All that’s required is a processor or receiver with a common 12V trigger connection.”

• Inputs: 1 XLR, 5 RCA
• Outputs: 1 RCA, 1 XLR
• THD+N at 1kHz = 0.0006% at 20-20kHz = 0.003% at DC to 1MHz: < 0.05 %
• S/N = 100dB at 20-20kHz S/N > 90dB at DC to 1MHz
• Frequency Response at 20-20kHz = +0.02dB/-0dB at DC to 1Mhz = +0.5dB/-0dB at DC-2.5 MHz +0/-3dB
• Maximum output: 7V RMS
• Phase shift = 0
• Input impedance = 10K ohm
• Output impedance = 100 ohm
• Dimensions : 17"W x 15"D x 1.97"H (2.56"H include feet)
• Weight: 17 lbs
• Power 120V 60Hz (100V and 240V models available)
Chassis available in black or silver anodized aluminum.
The P-20 has a three-year warranty.
• Ultra low noise 1nV/√ Hz JFETs
• Volume control features numerically controlled, switched-resistor ladder network with the latest in thin-film, ultra-low-noise resistor technology
• Full microprocessor control with memory retention
• No capacitor and no DC-servo in the signal path
• 3 separate power supplies
• Individual audio channels are shielded with heavy copper shield with thermal barrier
• Solid stainless steel back connector panel forms a solid signal ground reference
And there you have it.
382 South Abbott Avenue
Milpitas, CA 95035